This invention deals with a process to prepare aqueous solutions of betaine. This product is of value both as an animal feed and in the personal hygiene sector as a skin cleanser. The most common method for the preparation of betaine is by the reaction of trimethylamine with an alpha-halocarboxylic acid in the presence of an alkali metal hydroxide (for example see U.S. Pat. Nos. 4,497,825 and 5,292,942). There are several disadvantages to this method. For example, sodium chloride is always a co-product, and has to be removed(see U.S. Pat. No. 3,480,665). In addition to this, there is the concern of having the starting materials trimethylamine halocarboxylate as contaminants, and the process has to be modified to achieve low levels of trimethylamine.
U.S. Pat. 5,684,191 teaches a method for the combined synthesis of betaine and choline chloride from monochloroacetic acid, trimethylamine and ethylene oxide by first reacting trimethylamine with monochloroacetic acid and then reacting ethylene oxide with the reaction product of the previous step. As with the previously described processes, contaminants from the reaction are a problem. Other synthetic methods for the production of betaine are described in Gekkan Fudo Kemi Karu (1991), 7(6), 112-20.
Another route to prepare betaine is by the oxidation of choline [Me.sub.3 NCH.sub.2 CH.sub.2 OH].sup.+ using oxygen and an enzyme choline oxidase(see U.S. Pat. Nos. 5,187,088, 4,245,050, and 4,135,980). The oxidation produces 2 moles of hydrogen peroxide for each mole of betaine produced. Consequently, this method is not used to manufacture betaine, but is useful as an analytical technique to detect choline by measuring the generated hydrogen peroxide.
The oxidation of primary alcohols to the carboxylic acid salts using alkali metal hydroxide in the presence of precious metals such as Pd, Pt, Rh, Ru, Ir, Os, Re is well known (see Mallat, et al., "Oxidation of Alcohols With Molecular Oxygen on Platinum Metal Catalysts in Aqueous Solutions," Catalysis Today 19 (1994), 247-284). Japanese Patent No. 50-96516A discloses a process for the preparation of carboxylic acid salts by the liquid phase dehydrogenation of alcohols with caustic alkali in the presence of precious metals such as Pd. This process uses a high temperature, 100.degree. C.-270.degree. C., and uses alcohols such as diethylene glycol. The inherent disadvantage in this process is that high temperatures .gtoreq.100.degree. C. must be used and that the alkali metal salt of the desired acid is produced. There is literature, see Kirk Othmer Encyclopedia of Chemical Technology, Vol. 6, p 9, showing concentrated solutions of choline as the free base decompose at 100.degree. C. to give trimethylamine ethylene glycol and poly(ethylene glycol). Therefore one skilled in the art would expect such a molecule to degrade under the conditions of oxidation, high temperatures and alkaline solutions.